The present invention relates to a communication device and a communication method, each suitable in use for mobile communication equipment, typically, portable terminals (PDAs).
Conventionally, there is the technique of connecting a portable phone to a notebook personal computer (PC) or portable terminal (PDA), which uses a battery and can be readily carried, to exchange electronic mails or to have access to the Internet. Portable terminals, each incorporating a radio module, are available in the market. Such a portable terminal has made it possible to easily access servers through the Internet during movement.
For example, JP-A No. 145862/1998 discloses the radio data communication card that restricts the calling operation of a portable phone when the receive level of radio waves from a base station is less than a prescribed value. Moreover, JP-A No. 286324/1987 discloses the portable phone that reduces its transmission power when the output voltage value of the power source thereof drops, so that the serviceable life of the portable phone can be prolonged.
However, the above-mentioned previous techniques have the following disadvantages. Regarding the first problem, the constraint is performed when the reception level of radio waves of less than a prescribed value is checked at the time of starting communications. However, it is not stipulated that the transmission/reception level is checked after the starting of communications. For that reason, when the line is disconnected due to a decrease in reception level on a train or in a car, the connection between the terminal and a server on the network may be held in the current state. Thereafter, when an access to the server on the network is established after stabilization of the radio wave level, a double logging-on state occurs. As a result, the terminal may not be connected to the server for a fixed period.
Moreover, regarding to the second problem, the disclosed invention in which the transmission output is reduced when the output voltage value of the power source of mobile communication equipment drops provides the demerit to data communications. This approach increases error data, partial data missing, and an increased frequency of re-transmission on the network so that data cannot be stably transmitted and received on the network.